This is more of a curiosity question.... You know the nice plastic canister that virtually all 35mm films today come in? I understand, in the past, these used to be metal. To me, it looks like 35mm films are the type needing LEAST protection of this level. It already comes in a sturdy canister. A simple foil pack like 120 film should suffice to keep the film fresh. (may even be better because foil packages are hermetically sealed...) Anyone know technical or historical reason behind this?